Lecture Outline Introduction to experimental research Introduction to correlational research ...
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Transcript of Lecture Outline Introduction to experimental research Introduction to correlational research ...
Lecture Outline Introduction to experimental research
Introduction to correlational research
Three types of research validity
Class Activity
Experimental ResearchOverview and Major Features
An independent variable (IV) is manipulated A dependent variable(s) (DV) is measured Many basic experiments consist of two levels of the
independent variable experimental group control group
Control over extraneous variables holding constant randomizing effects
A causal relationship between the independent and dependent variables can be established
Basic Goal of Experimental Design Manipulate possible values of the IV
Observe behavioral changes as indexed by values of the DV
Basic Characteristics of Experimental Designs
Subjects are randomly assigned to research groups
A given participant must be equally likely to be assigned to any of the given groups
Random number table Flip a coin
In experimental designs, a causal relationship between the independent and dependent variables can be established
Independent Variable
Differing values of the IV are called “levels” May vary quantitatively
10 mg day 20 mg day
e.g. here are 2 levels of variable dosage
May vary qualitatively Zoloft Imipramine Prozac
e.g. here are 3 levels of the variable medication type
•An operational definition is a clearly defined set of procedures for measuring or manipulating the construct of interest.
•The key to an acceptable operational definition is that the procedure is specified precisely enough to allow replication by others.
Examples:quality of memory -- accuracy of recall in a certain taskdepression -- Beck Depression Inventory (survey) scorearousal -- galvanic skin response (conductivity of the surface of the skin)
Operational Definitions
She is a good carsalesperson
She:1. Sells many cars2. Points out + features3. Is nice4. Sells only good cars
Verbal StatementVerbal Statement Operational DefinitionOperational Definition
Operational Definitions: Examples
Stress
1. Environment/Number of stressors a. Number negative Life events b. Number of Examinations2. Self-report Measurable Nervous mood3. Behavior a. number of fidgets/minute b. Psychophysiological responses elevated
Verbal StatementVerbal Statement Operational DefinitionOperational Definition
Operational Definitions: Examples
Identify Key Experimental Features Social loafing refers to people’s tendency to slack
on group tasks. In one study on social loafing college participants cheered alone, and in groups of 2, 4, or 6 ppl. They were told to cheer as loud as possible at specific times so researchers could determine how much noise people made in social settings. The amount of noise made by each participant dropped as group size increased.
1) What is the IV? 2) What is the DV? 3) Why is random assignment important here?
Correlational Research: Major Features
No independent variables are manipulated
Two or more variables are measured and a relationship established
Correlational research does not show causality
Don’t confuse statistics with research design Correlation coefficients ( a statistic) can be used in correlational or
experimental research designs (although they are more commonly used in correlational designs)
Example of Non-Linear RelationshipYerkes-Dodson Law
Performance
Arousal
BetterBetter
WorseWorse
LowLowHighHigh
Correlation Does Not Imply Causation
Causality – must demonstrate that changes in one variable can only be due to influence of the other variable
Directionality of Effect Problem
Third Variable Problem
XX YY
XX YY
Class Class AttendanceAttendance
Higher Higher GradesGrades
Class Class AttendanceAttendance
Higher Higher GradesGrades
Directionality of Effect Problem
XX YY
XX YY
Aggressive BehaviorAggressive Behavior Viewing Violent TVViewing Violent TV
Aggressive BehaviorAggressive Behavior Viewing Violent TVViewing Violent TV
Aggressive children may prefer violent programs orViolent programs may promote aggressive behavior
Directionality of Effect Problem
Measurement Considerations Variables should be measured accurately
and consistently.
Accuracy Validity
Bathroom scale gives correct weight
Consistency Reliability
Bathroom scale gives same weight consistently
Evaluating Research: 3 Validities Validity
How accurate is the information from our research?
Three validities Construct validity Internal validity External validity
Construct Validity The degree to which the construct can be inferred from
the operational definition of that construct Never one perfect operationalization
Schacter and Singer (1962) Two-factor theory of emotion:
Emotions require arousal and label Factor 1: AROUSAL
Participants received epinephrine shots and either informed them of side-effects or not
Factor 2: LABEL Participants around "euphoric" or "angry“ confederate
How Valid are These Manipulations? Euphoria
Confederate shoots rubber bands, plays with hula hoops and crumples up paper and practices hook shots into wastebasket
Anger Confederate complains about the injection, adds
negative comments about the questionnaire they are filing out and ends up ripping up the questionnaire.
Simplified Results
Euphoria Euphoria ConditionCondition
Anger Anger ConditioConditio
nn
Informed of epinephrine effects
Uninformed of epinephrine effects
Internal and External Validity Internal validity
The extent to which the observed effect is caused only by the experimental treatment condition
The ability to draw conclusions about a causal relationship from our data
Experiments usually high in this External validity
The extent to which the results can be applied to and across different persons, settings and times
AKA generalizability Experiments often low in this
Generalizing From the Lab Setting Mundane realism
The extent to which an experiment is similar to real-life situations
Psychological realism The extent to which an experiment triggers relevant
psychological and group processes Key point
Lab experiments not automatically artificial When an experiment lacks mundane realism it may be
very realistic in terms of psychological realism
Assess Internal & External Validity
Does lighting affect productivity?
Study 1: Give people a production task in a
laboratory. The lab room is either bright or dim. Measure and compare their productivity (how quickly and accurately they perform the task).
Study 2: Give employees in a well-lit office and those
in a dim office a production task. Measure and compare their productivity (how quickly and accurately they perform the task).
The Tradeoff Real life situations
High external validity Hard to rule out other explanations
Low internal validity
Lab settings High internal validity Often artificial and findings can’t be
generalized Low external validity